Sub-mount for mounting optical component and light transmission and reception module

ABSTRACT

A sub-mount includes a recess for holding a polymer optical waveguide film and recesses for embedding and holding a light emitting element and a light detecting element. The sub-mount further has an adhesive filling groove formed adjacent to respective recesses. When mounting the polymer optical waveguide film, the light emitting element, and the light detecting element onto the sub-mount, an adhesive is accurately applied and is prevented from flowing out as the adhesive filling grooves are provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese patentdocument, No. 2005-207178, the disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sub-mount and to a light transmissionand reception module, more specifically, to a sub-mount mounted in apackage of an optical device and to a light transmission and receptionmodule using the same.

2. Description of the Related Art

Recently, in IC technique or LSI technique, optical wiring betweenequipments, between boards in the equipments, or in a chip is givenattention instead of the electrical wiring at high density to enhancethe operating speed or integration degree.

In Japanese Patent Application Laid-Open No. 2000-39530, for example, anoptical element including a light emitting element and a light detectingelement in a core clad stacking direction of a polymer optical waveguideincluding the core and the clad surrounding the core, and furtherincluding an incident side mirror where light emitted from the lightemitting element is coupled and a emission side mirror emitting thelight to the light detecting element. In the publication, the opticalelement is disclosed in which the clad layer is formed into a concaveshape at locations corresponding to the light paths from the lightemitting element to the incident side mirror, and from the emission sidemirror to the light detecting element, at where the light from the lightemitting element and the light from the emission side mirror converge.

Further, in Japanese Patent Application Laid-Open No. 2000-39531, anoptical element is disclosed in which light from a light emittingelement is coupled at a core end surface of a polymer optical waveguideincluding the core and a clad surrounding the core. In the opticalelement, the end surface of the core is formed into a convex surfacetowards the light emitting element so that the light from the lightemitting element is converged and a wave loss is suppressed.

Further, in Japanese Patent Application Laid-Open No. 2000-235127, anoptoelectronic integrated circuit is disclosed in which the polymeroptical waveguide circuit is directly assembled on the circuitintegrating the electronic elements and optical elements.

When the above elements are packaged in an optical wiring and can beincorporated into a device, the assembling flexibility of the opticalwiring can be increased. As a result, a light transmission and receptionelement with compact shape can be manufactured.

However, the methods proposed so far requires a mirror to be embedded toform a 90° return mirror, and requires positioning at high precisionwhen laminating the waveguide and the light transmission and receptionelement, and thus the cost required for mounting becomes large.

A polymer optical waveguide module equipped with light emitting anddetecting elements including a polymer optical waveguide film wasdisclosed by the present inventors (Japanese Patent Application No.2004-139041, Japanese Patent Application FE04-04966). In the disclosure,the polymer optical waveguide film includes a light path conversionmirror surface and an abutting surface on the same end.

A semiconductor laser device in which a mirror surface is formed on asub-mount of a semiconductor laser, wherein a light path of the laserlight is converted by such mirror surface is disclosed in JapanesePatent Application Laid-Open No. 2000-114655.

However, when mounting a light emitting element or a light detectingelement and a waveguide element in the sub-mount, an adhesive must beapplied to a predetermined position at excellent precision in case thatthe adhesive (including electrically conductive paste) is used forfixation. Further, the adhesive may flow out from a recess for mountingwhen the element is mounted.

The present invention provides a sub-mount for mounting an opticalcomponent in which the adhesive is applied to a predetermined positionat excellent precision and is prevented from flowing out, and in whichthe optical component is easily and reliably mounted; and a lighttransmission and reception module using the same.

SUMMARY OF THE INVENTION

The first aspect of the present invention provides a sub-mount formounting optical component comprising a recess for mounting forembedding and mounting the optical component, and an adhesive fillinggroove formed adjacent to the recess for mounting.

The second aspect of the present invention provides a light transmissionand reception module comprising an optical waveguide film formed with anoptical waveguide; a light transmitting section having a light emittingelement and a sub-mount for holding the light emitting element, thatholds one end of the optical waveguide film on the sub-mount so thatlight emitted from the light emitting element enters into an incidentend surface of the optical waveguide; and a light detecting sectionhaving a light detecting element and a sub-mount for holding the lightdetecting element, that holds the other end of the optical waveguidefilm on the sub-mount so that light emitted from an emission end surfaceof the optical waveguide is detected by the light detecting element.Each sub-mount includes a recess for mounting for embedding and mountingan optical component and an adhesive filling groove formed adjacent tothe recess for mounting.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail basedon the following figures, wherein:

FIGS. 1A to 1F are views showing manufacturing steps of a sub-mount ofthe present invention;

FIGS. 2A to 2D are views showing another manufacturing steps of asub-mount of the present invention;

FIG. 3 is a schematic configuration view of a light transmission andreception module according to the present embodiment;

FIGS. 4A and 4B are views showing follow-up property to deformation ofthe light transmission and reception module according to the presentembodiment;

FIG. 5A is a perspective view of an end portion of a polymer opticalwaveguide film of the light transmission and reception module accordingto the embodiment, FIG. 5B is a sectional view taken along A-A of FIG.5A, and FIG. 5C is a sectional view taken along B-B of FIG. 5B;

FIGS. 6A to 6I are views showing manufacturing steps of the polymeroptical waveguide film of the light transmission and reception moduleaccording to the embodiment;

FIG. 7A is a perspective view of the sub-mount of the light transmissionand reception module according to the present embodiment, FIG. 7B is aplan view of the sub-mount of the light transmission and receptionmodule according to the present embodiment, and FIG. 7C is a sectionalview taken along C-C of FIG. 7B;

FIG. 8A is a plan view of an optical transmission and reception sectionof the light transmission and reception module according to the presentembodiment, FIG. 8B is a sectional view taken along D-D of FIG. 8A, andFIG. 8C is a partially magnified view showing an optical coupler in FIG.8B in an enlarged manner;

FIG. 9 is a schematic view showing a configuration of the lighttransmission and reception module according to the present embodiment;

FIG. 10A is a perspective view of a sub-mount of another lighttransmission and reception module according to the present embodiment,FIG. 10B is a plan view of the sub-mount, and FIG. 10C is a sectionalview taken along C′-C′ of FIG. 10B;

FIG. 11A is a plan view of an optical transmission and reception sectionof another light transmission and reception module according to thepresent embodiment; FIG. 11B is a cross sectional view taken along D′-D′of FIG. 11A; FIG. 11C is a partially magnified view showing an opticalcoupler in FIG. 11B in an enlarged manner; and

FIG. 12 is a schematic view showing a configuration of another lighttransmission and reception module according to the present embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Sub-Mount and Its Manufacturing Method

The sub-mount of the present invention has a recess for embedding andmounting optical components and an adhesive filling groove arrangedadjacent to the recess for mounting. Noted that “the filling groovearranged adjacent” means inner spaces of the recess and the fillinggroove are communicated each other.

The sub-mount of the invention can be obtained by a manufacturing methodcomprising the steps of (1) a mold production step for producing a moldfor duplication having projections and recesses for replicating thesurface configuration of a sub-mount, (2) a filling step for filling theproduced mold with curing material, (3) a curing step for curing theapplied curing material, and (4) a releasing step for separating aduplicated sub-mount from the mold.

Methods of producing a mold (Step (1) above) include (A) a method bycuring liquid silicon rubber on a master plate of the sub-mount, (B) amethod by etching a silicon substrate, and (C) a method by casting ametal. The manufacturing method of the sub-mount using the mold producedin the method (A) will be referred to as “the duplication method usingsilicon resin” hereinafter, and the manufacturing method of sub-mountusing the mold produced by the method (B) or (C) will be referred to as“the stamper method” hereinafter.

Duplication Method Using Silicon Resin

An overall picture of duplication method using silicon resin isexplained by referring to FIGS. 1A to 1F. FIG. 1A shows a siliconsubstrate 50. Projections and recesses are formed on the main surface ofthe silicon substrate 50 by RIE, and a master plate 52 of a sub-mount isproduced (see FIG. 1B). By precision processing technology such as RIE,the master plate 52 of the sub-mount is produced precisely. Projectionsand recesses corresponding to a plurality of sub-mounts are formed inthe master plate, and by using this mater plate, a plurality of thesub-mounts can be duplicated simultaneously.

Liquid silicone rubber is applied or poured onto the projection andrecess formed surface of the master plate 52, and cured (see FIG. 1C).Then the silicone resin layer 54A is peeled off, and a silicone resinmold 54 having projections and recesses is obtained, in whichprojections and recesses replicate the surface configurations of thesub-mount (see FIG. 1D). Due to the adhering and releasing properties ofthe liquid silicone rubber, projections and recesses of the master plate52 are duplicated accurately. These steps correspond to the moldproduction step.

The mold 54 is filled with ultraviolet curable resin and cured byultraviolet irradiation (see FIG. 1E). These steps correspond to thefilling step and curing step. Then, by separating the cured resin layer56 from the mold 54, projections and recesses of the sub-mount surfaceare reproduced. This step corresponds to the releasing step. By dicingthis duplicate (not shown) into individual sub-mount, sub-mounts 58 ofultraviolet cured resin having projections and recesses on the surfaceare obtained (see FIG. 1F).

The principal steps of the duplication method using silicon resin aremore specifically described below.

(Production of Master Plate)

The above example is for producing the master plate of the sub-mount byetching the silicon substrate by RIE method. However, the material ofmaster plate is not limited to silicon substrate but may be glasssubstrate such as quartz glass substrate and metal substrate such asnickel (Ni) substrate and the like. For production of the master plate,conventional methods such as photolithography may be employed withoutany limitation. Moreover, the electrodeposition orphotoelectrodeposition previously filed by the present applicant(Japanese Patent Application No. 2002-10240) is also applicable forproduction of the master plate.

(Production of Mold)

In the duplication method using silicone resin, as mentioned above,liquid silicone rubber is applied or poured onto the projection andrecess formed surface of the produced master plate, dried if necessary,and cured, and a silicone resin layer is formed. By separating thesilicone resin layer from the master plate, a mold replicating thesurface configuration of the sub-mount is produced.

The thickness of the silicone resin layer is properly determined inconsideration of handling convenience of the mold, but in general it issuitably set to be about 0.1 to 50 mm. Preferably, the master plateshould be coated in advance with releasing agent or the like tofacilitate releasing from the mold.

The liquid silicone rubber is curing organopolysiloxane, which becomessilicone rubber after curing, and the term “liquid” includes paste orviscous substances. The liquid silicone rubber preferably containsmethyl siloxane group, ethyl siloxane group, or phenyl siloxane group inits molecule. Among liquid silicone rubber materials, liquid dimethylsiloxane rubber (polydimethyl siloxane: PDMS) is particularly preferablefrom the viewpoint of adhesion, releasing property, strength andhardness.

The liquid silicone rubber is excellent in both adhesion and separation,which are contradictory properties, and has a capability of replicatingfine configuration. Accordingly, the mold using silicone rubber iscapable of replicating the master plate at high precision, and it iseasy to separate the mold from ultraviolet curable resin for forming thesub-mount described later. Advantages of liquid silicone rubber moldinclude sufficient mechanical strength and dimensional stability as mold(which is to be used repeatedly), and stiffness (hardness) for retainingthe projected and recessed configurations. From this mold, therefore,sub-mounts retaining the shape at high precision can be reproduced veryeasily.

The liquid silicone rubber is preferred to be of two-pack type usedtogether with hardening agent. The addition type liquid silicone rubberis preferred because it is cured uniformly both at the surface and theinside in a short time, free from byproducts or produces few byproducts,is excellent in releasing property and small in shrinkage rate. Asrequired, various additives may be used in the liquid silicone rubber.

Since the liquid silicone rubber can be applied or poured on the surfaceof the master plate and the projections and recesses formed on themaster plate must be duplicated accurately, the viscosity is preferredto be less than a certain level. The viscosity of the liquid siliconerubber is preferred to be about 500 mPa.s to 7000 mPa.s, or morepreferably about 2000 mPa.s to 5000 mPa.s. For adjusting the viscosity,a solvent may be added slightly so as not to express adverse effects ofthe solvent.

The surface energy of mold is 10 dyn/cm to 30 dyn/cm, preferably 15dyn/cm to 24 dyn/cm, from the viewpoint of adhesion to the resin. Thesurface energy can be analyzed by measuring the contact angle betweensolid and liquid, and hence it is measured by a specified contact anglemeasuring apparatus. Share rubber hardness of the mold is 15 to 80,preferably 20 to 60, from the viewpoint of patterning performance,retaining of the recess shape and separation. Share rubber hardness canbe measured by using spring type rubber durometer for measuring anamount of deformation when a surface of the object is pushed by a needleand made deformed. Surface roughness of mold (maximum height: Ry) is setto be 0.2 μm or less, preferably 0.1 μm (100 nm) or less, from theviewpoint of patterning performance. Surface roughness Ry is a valueexpressing a maximum height defined by the difference of a maximum valueand a minimum value of roughness curve, and can be measured by probetype film thickness gauge.

The mold is preferred to be light transmittable in ultraviolet rayregion and/or visible ray region. When the mold is light transmittablein visible ray region, the state of filling the mold with the resin canbe observed and completion of filling is easily confirmed. When the moldis light transmittable in ultraviolet ray region, ultraviolet curing isachieved by making ultraviolet transmit through the mold. Thetransmittance of the mold in ultraviolet ray region (250 nm to 400 nm)is preferred to be 80% or more.

(Duplication of Sub-Mount)

In the duplication method using silicon resin, as mentioned above, themold replicating the surface configuration of the sub-mount is filledwith ultraviolet curable resin for forming a sub-mount, the appliedresin is cured, and the cured resin layer is separated from the mold, sothat a sub-mount forming projections and recesses on the surface can beduplicated.

As the ultraviolet curable resin for forming a sub-mount, a resin ofhigh heat resistance is preferred, and epoxy based and polyimide basedUV curable resins are preferably used. Also, monomer, oligomer, ormixture of monomer and oligomer of ultraviolet curing type may bepreferably used.

The ultraviolet curable resin is required to be sufficiently low inviscosity so as to fill up the projections and recesses of the mold. Theviscosity of ultraviolet curable resin is preferably 10 mPa.s to 2000mPa.s, more preferably 20 mPa.s to 1000 mPa.s, and most preferably 30mPa.s to 500 mPa.s.

To reproduce the projections and recesses formed on the master plate athigh precision, it is required that the volume change is small beforeand after curing of the ultraviolet curable resin. The volume change ispreferred to be 10% or less, or more preferably 6% or less. It ispreferred to avoid lowering the viscosity by using a solvent because thevolume change before and after curing becomes large.

To reduce volume change (shrinkage) after curing of the ultravioletcurable resin, a polymer may be added to the ultraviolet curable resin.The polymer to be added is preferably compatible with the ultravioletcurable resin and dose not have adverse effects on the resin refractiveindex, elasticity and light-transmitting properties thereof. By addingthe polymer, not only the volume change can be decreased, but also theviscosity or glass transition point of the cured resin can beeffectively controlled at advanced level. The polymer includes acrylicsystem, methacrylic acid system, epoxy system, and many others.

To cure the ultraviolet curable resin, light is emitted from ultravioletray lamp, ultraviolet ray LED, UV irradiation apparatus, in anultraviolet region (250 nm to 400 nm).

Stamper Method

A general picture of the stamper method is explained by referring toFIGS. 2A to 2D. In the stamper method, the mold is used as a stamp. FIG.2A shows a silicon substrate 60. Projections and recesses are formed onthe main surface of the silicon substrate 60 by RIE, and a silicon mold62 is produced (see FIG. 2B). This mold has projections and recessesduplicated corresponding to a plurality of sub-mounts, and by using thismold, a plurality of sub-mounts can be reproduced simultaneously. Byprecision processing technology such as RIE, the mold 62 accuratelyreplicating the projections and recesses of the sub-mount can beproduced precisely. These steps correspond to the mold production step.

Thermoplastic resin is tightly fitted to the mold 62, heated andpressurized, and cured by being cooled gradually (see FIG. 2C). Thesesteps correspond to the filling step and curing step. Then, byseparating the cured resin layer 64 from the mold 62, projections andrecesses of the sub-mount surface are reproduced. This step correspondsto the stripping step. By dicing this duplicate (not shown) intoindividual sub-mount, sub-mounts 66 of thermoplastic resin havingprojections and recesses on the surface are obtained (see FIG. 2D).

The principal steps of the stamper method are more specificallydescribed below. Hereinafter, in order to distinguish from the moldemployed in the duplication method using silicone resin, the moldproduced by the Stamper method is herein called the stamper.

(Production of Stamper)

The above example is for producing a stamper by etching a siliconsubstrate by RIE method. However, the material of the stamper is notlimited to silicon substrate, but may be glass substrate such as quartzglass substrate, and metal substrate such as nickel (Ni) substrate. Forproduction of the stamper, conventional methods such as photolithographymay be employed without any limitation. The stamper can be produced alsoby the electrodeposition or photoelectrodeposition previously filed bythe present applicant (Japanese Patent Application No. 2002-10240). Theproduction precision of the mold is enhanced by employingphotolithography or RIE.

(Duplication of Sub-Mount)

In the stamper method, as mentioned above, the stamper replicating thesurface configuration of the sub-mount is tightly fitted tothermoplastic resin for forming the sub-mount, heated and pressurized,and slowly cooled to ordinary temperature until cured. By releasing thecured resin layer from the mold, a sub-mount having projections andrecesses on the surface can be produced.

The thermoplastic resin for forming the sub-mount is desired to be highin heat resistance, and unsaturated polyester resin-based, epoxyresin-based, polyimide-based, PPS (polyphenylene sulfide)-basedthermoplastic resins are, in particular, preferably used. Further,ultraviolet curing monomer, oligomer, or mixture of monomer and oligomermay be used. A resin for precision molding obtained by mixing fillersinto thermosetting resin is also used preferably. An example of suchresin is BMC resin obtained by mixing fillers such as glass fiber inunsaturated polyester resin so as to suppress shrinkage.

The thermoplastic resin preferably has high dimensional precision with ashrinkage rate of 1% or less, thermal deformation starting temperatureof 200 deg. C. or more, is close to metal in coefficient of linearexpansion, and is easily combined with metal parts (smaller than inaluminum).

To form projections and recesses on the thermoplastic resin, thethermoplastic resin adhered to the stamper is heated to a temperatureabout glass transition point (Tg) +50 deg. C., and pressurized atpressure of about 10 N.

In the stamper method, low-melting glass which is molten by heating,such as glass which is softened (molten) at, for example, 600 deg. C. orless can be used instead of thermoplastic resin. The low-melting glassis heated to about 500 deg. C. and a metallic die is used as “stamper”,so that a sub-mount made of glass can be reproduced. Even a glassmaterial whose melting point is high, namely, 800 deg. C. such as Pyrex™is pressurized under heating temperature of about 650 deg. C., the glassmaterial is deformed so that a sub-mount can be reproduced by thestamper method. As the low-melting glass, hard glass mainly containingSiO₂ and B₂O₃ can be properly applied.

Light Transmission and Reception Module

FIG. 3 is a schematic structural diagram of light transmission andreception module in the embodiment. As shown in FIG. 3, the lighttransmission and reception module is composed of a belt-shaped polymeroptical waveguide film 10 and optical transmission and receptionsections 12, 14 for transmitting and receiving an optical signal throughan optical waveguide formed in the polymer optical waveguide film 10.

The optical transmission and reception section 12 has a sub-mount 22,and one end of the polymer optical waveguide film 10 is held on thesub-mount 22. The optical transmission and reception section 14 has asub-mount 24, and the other end of the polymer optical waveguide film 10is held on the sub-mount 24.

The polymer optical waveguide film 10 consists of a transparent resinfilm having flexibility, and has a follow-up property to deformationsuch as “bend” or “twist”, as shown in FIG. 4A and FIG. 4B. Thus, evenif the film is in a deformed state, the optical signal transmitted fromthe optical transmission and reception section 12 is guided through theoptical waveguide formed in the polymer optical waveguide film 10 andreceived by the optical transmission and reception section 14. Thepolymer optical waveguide film 10 preferably has a flexibility of acurvature radius of 3 mm or less. The curvature radius is a value that,when the microscopic portion of a curve formed on the inner side of thefilm when the film is bent approaches a circle, indicates the length ofthe radius of such circle, and the acceptable value thereof is measuredaccording to ASTM D-2176. The resin materials used for the polymeroptical waveguide film 10 will be hereinafter explained.

The polymer optical waveguide film 10 is preferred to have a thicknessin a range of 50 μm to 300 μm in order to enhance the follow-up propertyto deformation, and a more preferable range is 100 μm to 200 μm. For thesame reason, the width of the film is preferred to be in a range of 0.5mm to 10 mm, or more preferably 1 mm to 5 mm.

Polymer Optical Waveguide Film.

With referring to FIGS. 5A to 5C, the configuration of the polymeroptical waveguide film 10 will be described. FIG. 5A is a perspectiveview of an end portion of the polymer optical waveguide film 10, FIG. 5Bis a sectional view of A-A (section along optical axis of opticalwaveguide) of FIG. 5A, and FIG. 5C is a sectional view of B-B of FIG.5B.

As shown in the drawing, the polymer optical waveguide film 10 iscomposed of square cores 18 extending in film length direction, andcladding 16 and 20 surrounding the cores 18. In the polymer opticalwaveguide film 10, plural cores 18 are disposed parallel in the filmwidth direction and plural optical waveguides are formed in the film. Inthis example, two optical waveguides are formed in the film 10.

At the end of the polymer optical waveguide film 10, a mirror 10 b isdisposed at an angle of 45 degrees to the optical axis of opticalwaveguide. The mirror 10 b functions as optical path converter forconverting the optical path of the light guided in the opticalwaveguide. That is, the light guided in the optical waveguide has anoptical path thereof changed by 90 degrees on the mirror 10 b and isemitted from the film side 10 c of the light incident and exit surface.The leading end of the cladding 16 forming the mirror 11 b is cut offand an abutting surface 10 a orthogonal to the optical axis of opticalwaveguide is formed. The abutting surface 10 a is a surface abuttingagainst the sub-mount and is utilized in positioning on the sub-mount atthe time of mounting.

The polymer optical waveguide film 10 can be manufactured, for example,in the following steps (1) to (6): (1) a step of preparing a mold formedof a cured layer of curable resin for forming a mold, having recessescorresponding to the optical waveguide core portions and two or morethrough-holes each penetrating through both ends of the respectiverecess, (2) a step of tightly adhering a plastic film base material forcladding to the mold, the plastic film is capable of contacting tightlywith the mold, (3) a step of filling the through-hole at one end of therespective recess of the mold with a curable resin for forming a coreand evacuating and sucking from the through-hole at the other end of therespective recess resulting in each recess of the mold filled with thecurable resin, (4) a step of curing the filled curable resin for forminga core, and separating the mold from the plastic film base material forcladding, (5) a step of forming a cladding layer on the plastic filmbase material on which the cores are formed, and (6) a step of formingthe 45-degree mirror and the abutting surface at the end of the obtainedpolymer optical waveguide film.

The manufacturing processes of the above mentioned polymer opticalwaveguide film will now be further explained in detail with reference toFIG. 6A to FIG. 6I. To simplify the explanation, that in which oneoptical waveguide is arranged will be explained. FIG. 6A shows a masterplate 100 and numeral 120 denotes a projection corresponding to the coreof the optical waveguide. The curable resin for forming a mold isapplied or poured on the projection formed surface of the master plate100 and then cured (refer to FIG. 6B). In FIG. 6B, 200 a denotes acurable resin layer. Thereafter, when the curable resin layer 200 a ispeeled off, the curable resin layer 200 a formed with a recess isobtained (not shown). The through-holes 260 and 280 communicating to therecess 220 are formed in the curable resin layer 200 a by punching etc.at both ends of the recess to obtain a mold 200 (refer to FIG. 6C).

As shown in FIG. 6D, a plastic film base material for cladding 300 isadhered to the mold. A curable resin for forming a core is poured intothe through-hole 260 at the one end of the mold recess 220. The moldrecess 220 is filled with the curable resin for forming a core byevacuating and sucking from the through-hole 280 at the other end of themold recess 220. After the resin is cured, the mold is parted and a core320 is formed on the plastic film base material for cladding 300 asshown in FIG. 6E.

Forming a cladding (upper cladding layer) 400 (see FIG. 6F), the resinportions cured inside the through-holes 260 and 280 are cut off by adicer or the like, and a polymer optical waveguide film 10 is obtained(see FIG. 6G).

Finally, using a dicing saw having a 45-degree angle blade, the end ofthe polymer optical waveguide film 10 is diced, and a 45-degree mirror10 b is formed at the end of the film 10 (see FIG. 6H). Further, usingthe dicing saw, the leading end of the 45-degree mirror is cut off atright angle with respect to the longitudinal direction of polymeroptical waveguide film by a specified length including only the claddingportion, whereby an abutting surface 10 a is formed (see FIG. 6I).

The each step of forming the polymer optical waveguide film 10 isspecifically explained below.

(1) A Step of Preparing a Mold

Preferably, the mold is prepared by using a master plate havingprojecting portions corresponding to the optical waveguide cores but itis not limited to this. A method of using a master plate is explainedbelow.

(Production of Master Plate)

To produce the master plate having projecting portions, a conventionalmethod, for example, photolithography can be used without anylimitation. Also the method previously proposed by the present inventersfor producing a polymer optical waveguide by electrodeposition orphotoelectrodeposition (Japanese Patent Application No. 2002-10240) isalso applicable for production of the master plate.

The size of the projecting portions corresponding to the opticalwaveguide formed in the master plate is determined properly depending onthe application of the polymer optical waveguide. For example, in thecase of optical waveguide for single mode, a core of about 10 μm squareis generally used, or in the case of optical waveguide for multimode, acore of about 50 to 100 μm square is used, and depending on theapplications, an optical waveguide having much larger core of abouthundreds of μm may be used.

(Production of Mold)

As an example of production of mold, a layer of curable resin forforming a mold is formed on the projecting portion formed surface of themaster plate produced as mentioned above by applying or pouring curableresin for forming a mold thereon. The layer is dried and cured asrequired, then the cured resin layer is separated from the master plateand a die having recesses corresponding to the projecting portions areformed. The through-holes each communicating from one end to the otherend of the recess are formed in the die. The through-holes can be formedby punching the die in a specified shape. Even if the through-holes areformed by punching, the contact tightness between the mold and the filmbase material for cladding is excellent so that no gap to the film basematerial for cladding is formed except for the recess of the mold.Accordingly, the curable resin for forming a core will not permeate intoother portion than the recesses.

The thickness of the die (resin cured layer) is properly determined inconsideration of handling capability of the mold, but generally it issuitably set to be about 0.1 to 50 mm. Preferably, the master plateshould be preliminarily coated with releasing agent or the like tofacilitate releasing from the mold.

The through-hole provided at a supply side of the curable resin forforming a core functions as a reservoir for liquid (curable resin forforming a core). The through-hole provided at a discharge side of theresin is used for evacuation and suction to evacuate the recess so thatthe recess is filled with the resin. The shape and size of the supplyside through-hole are not particularly specified as far as thethrough-hole communicates with the supply side of the recess andfunctions as the liquid reservoir. The shape and size of the dischargeside through-hole are also unlimited particularly as long as thethrough-hole communicates with the discharge end of the recess and canbe used for evacuating and sucking.

Since the supply side through-hole functions as the reservoir for thecurable resin for forming a core, a section of the through-hole ispreferably formed to be made larger at the side contacting with the basematerial for cladding and smaller as away from the base material, sothat it is easier to separate the mold and base material after fillingthe recess with the curable resin for forming a core and curing. Thesectional configuration of the discharge side through-hole is notparticularly specified as the discharge side through-hole does notfunction as the reservoir.

As other example of producing the mold, the master plate is provided notonly with projecting portions corresponding to the optical waveguidecores but also with projecting portions for forming through-holes (theheight of the projecting portions are higher than the thickness of thecured layer of curable resin for forming a mold), and the curable resinfor forming a mold is applied to the master plate so that the projectingportions for forming the through-holes poke through the resin layer.After the resin layer is cured, the cured resin layer is separated fromthe master plate.

The curable resin for forming a mold is required to have appropriateproperties, including ease of peeling of the cured matter from themaster plate, sufficient mechanical strength and dimensional stabilityas mold (to be used repeatedly), stiffness (hardness) for retaining therecess shape, and adhesion to the film base material for cladding. Asrequired, various additives may be added to the curable resin forforming a mold.

The curable resin for forming a mold can be applied or poured to thesurface of the master plate and is required to replicate accurately theprojecting portions corresponding to the individual optical waveguidecores formed on the master plate. Therefore, it is preferred to haveviscosity below a certain limit, for example, about 500 to 7000 mPa.s.(The curable resin for forming a mold used in the invention includes amaterial becoming elastic rubber like body after curing.) For control ofviscosity, a solvent may be added slightly so as not to cause adverseeffects of the solvent

As the curable resin for forming a mold, a curable organopolysiloxane,which becomes silicone rubber (silicone elastomer) or silicone resinafter curing is preferably used from the viewpoint of releasingproperty, mechanical strength and dimensional stability, hardness andadhesion with base materials for cladding as stated above. The curingorganopolysiloxane is preferred to contain methyl siloxane group,ethylene siloxane group, or phenyl siloxane group in its molecule.

The curing organopolysiloxane may be either one-pack type or two-packtype to be used together with hardener, or may be either hot curing typeor cold curing type (for example, cured by moisture in air). Or otherhardener (ultraviolet curing agent) may be also used.

The curable organopolysiloxane is preferred to become silicone rubberafter curing. So-called liquid silicone rubber can be used (the term“liquid” includes paste or highly viscous substances herein) and thetwo-pack type to be used together with hardener is preferred. Above all,the addition type liquid silicone rubber is especially preferred becauseit is cured in short time uniformly both on surface and inside thereof,free from byproducts or produce few byproducts, and excellent inreleasing property and small in shrinkage rate.

Among liquid type silicone rubbers, liquid dimethyl cyclohexane rubberis particularly preferable from the viewpoint of adhesion, separation,strength and hardness. The cured substance of liquid dimethylcyclohexane rubber is generally low in refractive index of about 1.43,and a mold made from this substance can be preferably used as claddinglayer directly, which does not cause separation from the base materialfor cladding. In this case, it is required to have proper means toprevent peeling of applied core forming resin and base material forcladding from the mold.

The viscosity of liquid silicone rubber is preferably about 500 to 7000mPa.s, or more preferably about 2000 to 5000 mPa.s, from the viewpointof accurate replicating of projecting portions corresponding to theoptical waveguide cores and the position regulating portions of thepower supply wire, ease of defoaming by limiting entry of foams, andobtaining mold size of several millimeters in thickness.

A surface energy of the mold is in a range of 10 dyn/cm to 30 dyn/cm,preferably 15 dyn/cm to 24 dyn/cm from the viewpoint of the adhesionwith the base material film. The surface energy is measured by a methodof measuring a critical surface tension using a Zisman method. Sharerubber hardness of the mold is 15 to 80, or preferably 20 to 60 from theviewpoint of profiling performance, maintenance of the recess shape andseparation. The share rubber hardness can be measured according to JIS K6253 by using a durometer.

A surface roughness of the mold (an arithmetic mean roughness Ra) is 0.2μm or less, or preferably 0.1 μm or less from the viewpoint of profilingperformance. The arithmetic mean roughness Ra can be measured accordingto JIS B 0601.

The mold is preferred to be light transmittable in ultraviolet rayregion and/or visible ray region. When the mold is light transmittablein visible ray region, positioning is easier when adhering the mold tothe film base material for cladding at step (2) below, and filling ofmold recess with curable resin for forming a core can be observed atstep (3) so that completion of filling can be easily known.

When the mold is light transmittable in ultraviolet ray region,ultraviolet curing is to be achieved by transmitting ultraviolet throughthe mold in case that ultraviolet curable resin is used to form a core.Preferably, the transmittance of the mold in ultraviolet ray region (250nm to 400 nm) is 80% or more.

The curable organopolysiloxane, in particular, liquid silicone rubberwhich becomes silicone rubber after curing is excellent in both of thecontradictory properties of adhesion and separation with respect to thefilm base material for cladding and has a capability of replicating nanoconfiguration, and also works to prevent entry of liquid when siliconerubber and cladding base material are adhered.

As the mold using such silicone rubber copies the master plateaccurately and adheres to the cladding base material, it fills only therecess between the mold and cladding base material efficiently with thecore forming resin, and the mold can be separated easily from thecladding base material. Therefore, polymer optical waveguides retainingthe configurations thereof at high precision can be produced veryeasily.

(2) A Step of Tightly Adhering a Plastic Film Base Material for Claddingto the Mold

Since an optical device (a light transmission and reception module)produced from the polymer optical waveguide of the invention is used inoptical wiring in various layers, the material of the plastic film basematerial for cladding is properly selected in consideration ofrefractive index, light permeability and other optical characteristics,mechanical strength, heat resistance, adhesion with mold, flexibilityand others, depending on the applications of the optical device.

Examples of the film include alicyclic acrylic resin film, alicyclicolefin resin film, triacetic cellulose film, and fluorine containingresin film. The refractive index of film base material is preferably1.55 or less, or more preferably 1.53 or less, in order to keep enoughdifference in refractive index from the core.

The alicyclic acrylic resin film is, for example, OZ-1000, OZ-1100(Hitachi Chemical Co., Ltd.) manufactured by introducing tricyclodecaneor other alicyclic hydrocarbon in ester substituent.

The alicyclic olefin resin film is one having norbornene configurationin the main chain, and one having norbornene configuration in the mainchain and having polar group such as alkyl oxycarbonyl group (alkylgroup having 1 to 6 carbon atoms or cycloalkyl group) in the side chain.Above all, the alicyclic olefin resin having norbornene configuration inthe main chain and having polar group such as alkyloxycarbonyl group inthe side chain as mentioned above is particularly suited to productionof optical waveguide sheet of the invention because it is excellent inoptical characteristics, having low refractive index (refractive indexbeing about 1.50, assuring a sufficient difference in refractive indexbetween core and cladding) and high light permeability, excellent inadhesion to the mold, and excellent in heat resistance.

A thickness of the film base material is properly selected inconsideration of flexibility, rigidity and ease of handling, and isgenerally about 0.1 mm to 0.5 mm.

(3) A Step of Filling a Curable Resin for Forming a Core in the Recessof the Mold

At this step, the through-hole provided at the supply side of the resinis filled with curable resin for forming a core, and by evacuating andsucking through the through-hole provided at the discharge side of theresin, the gap (i.e., the recess of the mold) formed between the moldand the film base material for cladding is filled with the resin. Byevacuating and sucking, the adhesion of the mold and the film basematerial for cladding is enhanced, and entry of foams can be avoided.For evacuating and sucking, a suction pipe connected to a pump isinserted into the through-hole at the discharge side.

The curable resin for forming a core includes resins of radiation curingtype, electron curing type and heat curing type, and above all theultraviolet curable resin and thermosetting resin are preferably used.As the ultraviolet curable resin and thermosetting resin for forming acore, ultraviolet curing type and thermosetting type monomer, oligomer,or mixture of monomer and oligomer may be preferably used. Ultravioletcurable resins of epoxy system, polyimide system, and acrylic system mayalso be preferably used.

The curable resin for forming a core is filled in gaps (the recesses ofmold) formed between the mold and the film base material by capillarity,and the curable resin for forming a core is required to be sufficientlylow in viscosity for realizing such filling. Therefore, the viscosity ofthe curable resin is 10 mPa.s to 2000 mPa.s, preferably 20 mPa.s to 1000mPa.s, or more preferably 30 mPa.s to 500 mPa.s.

Besides, in order to reproduce the original shape of the projectingportion corresponding to the optical waveguide core formed on the masterplate at high precision, it is important that the volume change is smallbefore and after curing of the curable resin. For example, decrease involume leads to conduction loss. Therefore, the curable resin forforming a core is desired to be small in volume change as far aspossible, for example, 10% or less, or preferably 6% or less. It isrecommended to avoid lowering of viscosity by using a solvent as thevolume change becomes large before and after curing.

To reduce the volume change (shrinkage) after curing of the resin, apolymer may be added to the resin. Such a polymer is preferred as beingcompatible with curable resin for forming a core, not having adverseeffects on the resin refractive index, elasticity or permeability. Byadding the polymer, not only the volume change can be decreased, butalso it is effective to control the viscosity or glass transition pointof the cured resin at an advanced level. The polymer includes acrylicsystem, methacrylic system, epoxy system, and many others.

The refractive index of the cured matter of curable resin for forming acore is required to be larger than that of the film base material as thecladding (including the cladding layer in step (5) below), and is 1.50or more, preferably 1.53 or more. The difference in refractive indexbetween the cladding (including the cladding layer in step (5) below)and the core is 0.01 or more, preferably 0.03 or more.

(4) A Step of Curing the Applied Resin for Forming a Core and Separatingthe Mold from the Film Base Material for Cladding

At this step, the applied curable resin for forming a core is cured. Tocure the ultraviolet curable resin, ultraviolet lamp, ultraviolet LED,UV irradiation equipment or the like is used, and to cure thethermosetting resin, it is heated in an oven or the like.

The mold used at steps (1) to (3) may be directly used as the claddinglayer as far as the conditions such as refractive index are satisfied,and in such a case, separation of the mold is not required. In thiscase, it is preferred to treat the mold in ozone in order to enhance theadhesion between the mold and core material.

(5) A step of Forming a Cladding Layer on the Plastic Film Base Materialfor Cladding

A cladding layer is formed on the film base material on which the coresare formed. The cladding layer to be used may be the film base materialfor cladding used in above step (2), a layer formed by applying andcuring a curable resin for cladding, and a polymer film obtained byapplying and drying a solvent solution of polymer membrane. As thecurable resin for cladding, ultraviolet curable resin or thermosettingresin is used preferably, and for example, monomer, oligomer or mixtureof monomer and oligomer of ultraviolet curing type or thermosetting typemay be used.

To reduce a volume change (shrinkage) after curing of the resin, theresin may be blended with a polymer (for example, methacrylic system,epoxy system), which is compatible with the resin and does not haveadverse effects on resin refractive index, elasticity or permeability.

When using a film as cladding layer, an adhesive may be used. Therefractive index of the adhesive is desired to be closer to therefractive index of the film. As the adhesive, the ultraviolet curingtype resin or thermosetting resin is used preferably. For example,monomer, oligomer or mixture of monomer and oligomer of ultravioletcuring type or thermosetting type may be used. To reduce the volumechange (shrinkage) after curing of ultraviolet curable resin orthermosetting resin, the same type polymer added to the cladding layermay be used.

The refractive index of the cladding layer is desired to be 1.55 orless, preferably 1.53 or less in order to assure a sufficient differencein refractive index from the core. From the viewpoint of entrapping thelight, the refractive index of the cladding layer is preferred to besimilar to the refractive index of the film base material.

(6) A Step of Forming a 45-degree Mirror and an Abutting Surface on anEnd Surface of the Obtained Polymer Optical Waveguide Film

The obtained polymer optical waveguide film is constituted so that the45-degree mirror and the abutting surface are formed on the film endsurface by using, for example, a dicing saw. The core portion is exposedfrom the mirror.

Since the plastic film base material exhibits favorable adhesion to themold, no gap except for the recess configuration formed in the mold isallowed between the mold and the cladding base material without fixingthem by using special means but adhering the plastic film base materialfor cladding tightly to the mold. Accordingly, the curable resin forcuring a core can be provided only in the recess.

Therefore, the manufacturing process is extremely simplified and thepolymer optical waveguide film can be manufactured at an extremely lowcost.

In this manufacturing method, through-holes are provided in the mold andthe discharge side of the recess of the mold is evacuated and suckedthrough the through-holes so that the adhesion of the mold and the filmbase material is further enhanced, and entry of foams can be avoided.Further, although performing such a simple method, the obtained polymeroptical waveguide film has small conduction loss and high precision, andcan be mounted in various devices.

Optical Transmission and Reception Section

Referring to FIGS. 7A to 7C and FIGS. 8A to 8C, a configuration of anoptical transmission and reception section 12 having a sub-mount 22 isexplained. As a sub-mount 24 is same as the sub-mount 22 inconfiguration and an optical transmission and reception section 14 isthe same as the optical transmission and reception section 12 inconfiguration, the detailed description of the sub-mount 24 and theoptical transmission and reception section 14 will be omitted.

First, referring to FIGS. 7A to 7C, the configuration of the sub-mount22 is explained. FIG. 7A is a perspective view of the sub-mount 22, FIG.7B is a plan view of the sub-mount 22, and FIG. 7C is a sectional viewC-C of FIG. 6B.

The sub-mount 22 is made of a rectangular parallelepiped substrate. Thissub-mount 22 has a recess 26 (a recess for mounting optical components)for mounting a polymer optical waveguide film 10, and recesses 28 a and28 b (recesses for mounting optical components) for fitting and holding(mounting) a light detecting element and a light emitting element,respectively. In this embodiment, two recesses 28 a and 28 b are formedto mount the respective element, however, one recess may be formed tomount both of a light detecting element and a light emitting element.The recess 26 includes an applied surface 26 a attached to the abuttingsurface 10 a of the polymer optical waveguide film 10, and a mountingsurface 26 b for mounting a film surface 10 c of the polymer opticalwaveguide film 10.

Adhesive filling grooves 27, 29 a and 29 b are formed adjacent to eachof the recesses 26, 28 a, and 28 b serving as recesses for mountingoptical component, respectively.

In part of the surface of the sub-mount 22, electrode films 30 a, 30 b,30 c, 30 d are formed for electrical wiring with the light detectingelement and the light emitting element. In this example, the electrodefilms 30 a, 30 b are patterned so as to be extended to the top surfaceof the sub-mount 22 from the bottom surface of the recess 28 by way ofthe side surface.

The electrode films 30 c, 30 d are patterned on the top surface of thesub-mount 22 so as to be insulated from the electrode films 30 a, 30 b.By forming the electrode films at the sub-mount 22, electrical wiring iseasily provided to the light detecting element and the light emittingelement when installing the light transmission and reception module in apackage.

The sub-mount 22 is produced at a high precision by the manufacturingmethod using the above-mentioned duplication method with the mold. Theelectrode films 30 a, 30 b, 30 c, 30 d are, for example, formed byvapor-depositing a metal film of gold (Au), aluminum (Al) or the like onthe surface of sub-mount 22, and patterning this metal film by thetechnology of photolithography.

Referring next to FIGS. 8A to 8C, a mounting state of an opticaltransmission and reception section 12 is explained. FIG. 8A is a planview of the optical transmission and reception section 12, FIG. 8B is asectional view taken along D-D (sectional view along the optical axis ofoptical waveguide) of FIG. 8A, and FIG. 8C is a partially magnified viewshowing an optical coupler in FIG. 7B.

When mounting the light transmission and reception module, a surfaceemission type semiconductor laser diode (LD) 32 as the light emittingelement, a photo diode (PD) 34 as the light detecting element, and thepolymer optical waveguide film 10 are held on the sub-mount 22 of theoptical transmission and reception section 12.

The end of the polymer optical waveguide film 10 is fitted into therecess 26 of the sub-mount 22. The abutting surface 10 a abuts againstthe applied surface 26 a of the sub-mount 22 and is positioned atspecified location. The film surface 10 c of the light incident and exitside is mounted on the sub-mount 22 so as to oppose to the mountingsurface 26 b of the sub-mount 22. Thus, holding the polymer opticalwaveguide film 10 on the mounting surface 26 b, the flexible polymeroptical waveguide film 10 can be held stably.

The film surface 10 c is adhered to the opposing mounting surface 26 b,the LD 32 and the PD 34 with the adhesive 36 filled from the adhesivefilling groove 27. A light curable adhesive such as ultraviolet curableresin, a heat curable adhesive or the like is used as the adhesive 36,but the same curable resin used for the clad 16 of the polymer opticalwaveguide film 10 is preferably used to reduce light loss.

The LD 32 and the PD 34 are fitted in the recesses 28 a and 28 b of thesub-mount 22, respectively and are fixed at the bottom surface of therecesses 28 a and 28 b. By fitting the LD 32 and the PD 34 in therecesses 28 a and 28 b, the optical transmission and reception section12 is made compact. In this example, the electrode films 30 a and 30 bare formed in the bottom surfaces of the recesses 28 a and 28 b.Therefore, the back electrode of the LD 32 and the electrode film 30 a,and the back electrode of the PD 34 and the electrode film 30 b arefixed at the bottom surfaces of the recesses 28 a and 28 b by conductivesolder (electroconductive paste) or the like which is filled through theadhesive filling grooves 29 a and 29 b so as to conduct with each otherelectrically.

The other electrode of LD 32 is electrically connected to the electrodefilm 30 c by wire 38 a, and the other electrode of PD 34 is electricallyconnected to the electrode film 30 d by wire 38 b.

The LD 32 and PD 34 are disposed at specified positions, depending onthe abutting position of the abutting surface 10 a, so that the emitter32 a of the LD 32 is opposite to the end surface (incident end surface)of the core 18 of the optical waveguide for transmission of polymeroptical waveguide film 10, and that the detector 34 a of the PD 34 isopposite to the end surface (exit end surface) of the core 18 of opticalwaveguide for reception of polymer optical waveguide film 10.

Herein, the optical waveguide for transmitting an optical signal fromthe optical transmission and reception section 12 is described as theoptical waveguide for transmission, and the optical waveguide forreceiving an optical signal from the optical transmission and receptionsection 12 is described as the optical waveguide for reception. As seenfrom the optical transmission and reception section 14, needless to say,the optical waveguide for transmission and optical waveguide forreception are inverted.

The optical transmission and reception section 12 can be assembledeasily, by fitting the LD 32 and PD 34 in the recesses 28 a and 28 b ofthe sub-mount 22 and fitting the polymer optical waveguide film 10 inthe recess 26 of the sub-mount 22.

In this embodiment, the polymer optical waveguide film 10 is composed ofa transparent resin, and the position of end of the core 18 of theoptical waveguide can be observed through back surface reflection of themirror 10 b. Therefore, by using the back surface reflection image onthe mirror 10 b, alignments of LD 32 and PD 34 become easy to be mountedin high precision by passive alignment.

Operation of Light Transmission and Reception Module

Referring to FIG. 9, the operation of the light transmission andreception module of the embodiment is explained. FIG. 9 is a viewschematically showing a structure of light transmission and receptionmodule. Herein, the optical waveguide for transmitting an optical signalfrom the optical transmission and reception section 12 is designated asthe optical waveguide for transmission, and the optical waveguide forreceiving an optical signal from the optical transmission and receptionsection 12 is designated as the optical waveguide for reception.

In the light transmission and reception module of the embodiment, whentransmitting an optical signal from the optical transmission andreception section 12 to the optical transmission and reception section14, the light emitted from the LD 32 held on the sub-mount 22 of theoptical transmission and reception section 12 enters into the incidentend surface of the core 18 of the optical waveguide for transmission,and is guided in the optical waveguide for transmission formed in thepolymer optical waveguide film 10. The light emitted from the exit endsurface of the core 18 of the optical waveguide for transmission isreceived in the PD 34 held in the sub-mount 24 of the opticaltransmission and reception section 14.

Similarly, when receiving an optical signal transmitted from the opticaltransmission and reception section 14 by the optical transmission andreception section 12, the light emitted from the LD 32 held in thesub-mount 24 of the optical transmission and reception section 14 entersinto the incident end surface of the core 18 of the optical waveguidefor reception, and is guided in the optical waveguide for receptionformed in the polymer optical waveguide film 10. The light emitted fromthe exit end surface of the core 18 of optical waveguide for receptionis received in the PD 34 held in the sub-mount 22 of the opticaltransmission and reception section 12.

As explained above, in the light transmission and reception module ofthe embodiment, two way light communications are performed between a setof optical transmission and reception sections as mentioned above. Theflexible belt-shaped polymer optical waveguide film has a property offollowing up the deformation such as bending, folding or twisting, sothat even if the film is deformed, optical signal can be transmitted andreceived by way of the optical waveguide formed in the polymer opticalwaveguide film. Therefore, it can be used in optical wiring ofoften-bent-or-folded connection of cellphone, slim personal computer orother mobile appliance.

In the light transmission and reception module of the embodiment, sincethe electrode film is formed in the sub-mount, when installing the lighttransmission and reception module in a package, electrical wiring can beeasily provided in the light detecting element and in the light emittingelement of the optical transmission and reception section.

In the light transmission and reception module according to the presentembodiment, since the sub-mount including adhesive (includingelectrically conductive paste) filling grooves 27, 29 a and 29 badjacent to the recesses 26, 28 a and 28 b for mounting opticalcomponent is used as described above, the adhesive is evenly applied tothe bottom surfaces (component mounting surface) of the recesses 26, 28a and 28 b by being poured from the adhesive filling grooves 27, 29 aand 29 b. When the optical components are mounted to the recesses 26, 28a and 28 b, the adhesive filling grooves 27, 29 a and 29 b function asthe reservoir thereby preventing the adhesive from flowing out.

Another Arrangement of Electrode

In the embodiment, it is explained that the electrode film is formed soas to extend from the bottom surface of the recess formed on thesub-mount via the side surface to the top surface of the sub-mount andthe rear electrodes of LD and PD and the electrode films areelectrically conductive, but the forming pattern of the electrode filmsis not limited to this.

For example as shown in FIGS. 10A to 10C, FIGS. 11A to 11C and FIG. 12,electrode films 40 a, 40 b, 40 c and 40 d which are insulated from eachother are formed on the top surface of the sub-mount 22. When the lighttransmission and reception module is mounted, the electrode films 40 aand 40 b may be electrically connected to the electrodes of the LD 32 bywires 42 a and 42 b, and the electrode films 40 c and 40 d may beelectrically connected to the electrodes of the PD34 by wires 42 c and42 d.

Another Constitution of Module

In the embodiment, it is explained that the light transmission andreception module of two way optical communications having the lighttransmission and reception sections respectively mounted with both thelight emitting element and the light detecting element. However, thelight transmission and reception module may be one way type which isconstituted with a light transmission section having a light emittingelement and a light reception section having a light detecting element.

EXAMPLES

The invention is more specifically described below by referring toexamples, but the invention is not limited to these examples alone.

Example 1

Sub-mounts are produced with “Duplication Method using Silicone Resin”and the light transmission and reception module shown in FIG. 3 isproduced.

(Production of Polymer Optical Waveguide Film)

After an Si substrate is coated with a thick film resist (trade name:SU-8, manufactured by Microchemical) according to a spin coat method, itis prebaked at 80 deg. C., is exposed through a photomask and isdeveloped so that four projections having a quadrate section (width: 50μm, height: 50 μm, length: 80 mm) are formed. Each gap between theprojections is set to 250 μm. The Si substrate coated with the thickfilm resist is post-baked at 120 deg. C., so that a master plate formanufacturing a polymer waveguide is produced.

A releasing agent is applied on the master plate, and a mixture ofthermosetting liquid dimethyl siloxane rubber (product name: SYLGARD184manufactured by Dow-Corning Asia, viscosity 5000 mPa.s) and itshardening agent is poured in, and heated and cured for 30 minutes at 120deg. C. After releasing, a die (die thickness: 5 mm) having recessescorresponding to the projections of a rectangular section is produced.

Further, through-holes of circular top view, having a section tapered inmold thickness direction are formed by punching to communicate with therecesses at both ends of each recess, whereby a mold is produced.

This mold is adhered tightly to a film base material for cladding(product name: Arton Film manufactured by JSR Co., refractive index1.510) of film thickness of 50 μm, which is one size larger than themold.

A few drops of ultraviolet curable resin of viscosity of 500 mPa.s aredropped into supply side through-hole of the mold, and the dischargeside (i.e., the evacuating and sucking side) through-hole is evacuatedand sucked, such that the recess is filled with the ultraviolet curableresin in 10 minutes. It is cured by emitting ultraviolet light of 50mW/cm² irradiated from outside of the mold for 5 minutes, and the moldis separated from Arton Film, whereby cores of same shapes as projectingportions of the master plate are formed on the Arton Film.

The ultraviolet curable resin with the same refractive index of 1.510after curing as that of the Arton film is applied to the core formedsurface of the Arton film, and the film base materials for cladding of50 μm are laminated. The ultraviolet curable resin is cured by emittingultraviolet light of 50 mW/cm2 for five minutes so that two films areadhered, thereby a belt-shaped polymer optical waveguide film with widthof 1.5 mm and thickness of 180 μm is obtained.

Using a dicing saw with a Si blade angled by 45 degrees, both ends ofthis polymer optical waveguide film are cut off at an angle of 45degrees with respect to the optical axis, such that each core having a45-degree mirror surface is exposed. Each cladding portion of the45-degree mirror surfaces is cut off vertically to the optical axis at aposition of 50 μm inside from the leading end, and a polymer opticalwaveguide film having 45-degree mirror surfaces and vertical cutsections at both ends is obtained.

(Production of Sub-Mount)

On Si substrate of 600 μm in thickness, two recesses for mounting lightemitting element and light detecting element are formed by RIE. Thedepth of recess is 250 μm. Further, to mount the polymer opticalwaveguide film, a recess of 50 μm in depth having an applied surfaceopposing to the vertical cut section of the polymer optical waveguidefilm is formed by RIE method. Adhesive filling grooves in whichconductive paste or adhesive is poured are formed adjacent to theserecesses, respectively. The Si master substrate having the recesses isprepared as a master plate of the sub-mount. In this master plate,recesses for a plurality of sub-mounts are formed and, at each recess,portions corresponding to the filling grooves for the adhesive or theconductive paste are formed. By using this master plate, a plurality ofsub-mounts can be reproduced simultaneously.

On this master plate, a mixture of thermosetting liquid dimethylsiloxane rubber (product name: SYLGARD184, manufactured by Dow-CorningAsia, viscosity 5000 mPa.s) and its hardening agent is poured in, andheated and cured for 30 minutes at 120 deg. C. After releasing the curedlayer, a silicone resin mold (die thickness: 5 mm) having projectionsand recesses corresponding to the projections and recesses of the masterplate on its surface is produced.

Ultraviolet curable resin (of NTT-AT) with viscosity of 3000 mPa.s isapplied, and ultraviolet light of 50 mW/cm² is irradiated from outsideof the mold for 5 minutes to cure, and the cured resin layer is releasedfrom the mold. After vapor-depositing Au in a thickness of 200 nm on thecured resin layer, the Au electrodes are patterned by photolithography,whereby electrode pads for lower electrodes extending from a bottomsurface to a side surface of each recess up to a top surface of thesub-mount, electrode pads for upper electrodes insulated from theelectrode pads for lower electrodes, and electrode pads for the electricsupply wires are formed. By cutting the cured resin layer havingelectrode pads by using a dicer, a plurality of sub-mounts A made ofultraviolet curable resin are formed.

Dimensional difference of projections and recesses as seen from themaster plate of the sub-mount (the master substrate) is within 100 nm,and sub-mounts A made of ultraviolet curable resin can be produced athigh precision.

(Mounting of Module)

The recess for the light emitting element of the sub-mount A is filledwith conducting paste (trade name: SA-0425, manufactured by FUJIKURAKASEI CO., LTD.) through the adhesive filling groove by a dispenser, anda VCSEL element (manufactured by Fuji Xerox, Co., Ltd.) is placed. Therecess for the light detecting element of the sub-mount A is filled withthe conducting paste (product name: SA-0425, manufactured by FUJIKURAKASEI CO., LTD.) through the adhesive filling groove by a dispenser, anda photodiode element is placed. After each element is disposed, thesub-mount A is heated to 180 deg. C. for 30 minutes so that the VCSELelement and the photodiode element are fixed to the predeterminedrecesses of the sub-mount A, respectively. As a result, each lowerelectrode of the VCSEL element and the photodiode element iselectrically connected to the electrode pad. Thereafter, the respectiveupper electrode of the VCSEL element and the photodiode element and theelectrode pads are bonded by using an Au wire.

Both ends of the polymer optical waveguide film having 45-degree mirrorsare respectively fitted into the recesses of the sub-mounts A, each ofthe vertical cut section is positioned by abutting against the appliedsurface of the sub-mount A, and polymer optical waveguide film is fixedto sub-mount A by using ultraviolet curing agent (adhesive) which isfilled through the adhesive filling groove. As a result, a two-way lighttransmission and reception module having a pair of optical transmissionand reception sections and polymer optical waveguide film is obtained.

(Evaluation of Communication Performance)

Light transmission and reception performance of a two-way lighttransmission and reception module which is obtained according to Example1 was evaluated by using a sampling oscilloscope (product name: Agilent86100C, manufactured by Agilent Technologies) and a pulse patterngenerator. As a result, satisfactory eye pattern could be measured at upto 3.125 Gbps.

Example 2

The sub-mount made of resin is produced through “Stamper Method”, andthe light transmission and reception module shown in FIG. 3 is produced.The light transmission and reception module is produced using the methodsimilar to Example 1 except that producing the sub-mount with “StamperMethod”.

(Production of Sub-Mount)

The master substrate made of Si is produced similar to Example 1. Themaster substrate is used as the stamper (mold) and the thermoplasticbulk molding compound (BMC) resin is adhered to the stamper, heated fortwo minutes under a pressure of 100 N and at a temperature of 250 deg.C., and thereafter, stood to cool to cure the epoxy resin. The curedlayer is then stripped from the stamper, thereby producing the curedresin layer (thickness of mold: 5 mm), which surface includesprojections and recesses corresponding to the projections and recessesof the stamper.

Next, after vapor depositing Au on the cured resin layer at a thicknessof 200 nm, Au electrode patterning is performed with photolithography,thereby forming an electrode pad for the lower electrode extending fromthe bottom surface of each recess to the upper surface of the sub-mountthrough the side surface, and an electrode pad for the upper electrodeinsulated from the electrode pad for the lower electrode. The curedresin layer formed with the electrode pads is cut with a dicer to form aplurality of sub-mounts C made of epoxy resin.

Dimensional difference of projections and recesses as seen from thestamper (the master substrate) is within 100 nm, and sub-mounts C madeof ultraviolet curable resin can be produced at high precision.

(Mounting of Module)

A two-way light transmission and reception module comprising a pair ofoptical transmission and reception sections and a polymer waveguide filmis obtained by mounting in a manner similar to Example 1 with thesub-mount C.

(Evaluation of Communication Performance)

Light transmission and reception performance of a two-way lighttransmission and reception module which is obtained according to Example2 was evaluated by using a sampling oscilloscope (product name: Agilent86100C, manufactured by Agilent Technologies) and a pulse patterngenerator. As a result, satisfactory eye pattern could be measured at upto 3.125 Gbps.

Example 3

A sub-mount made of glass is produced through “Stamper Method”, and thelight transmission and reception module shown in FIG. 3 is produced. Thelight transmission and reception module is produced using the methodsimilar to Example 2 except that producing the sub-mount made of glassthrough “Stamper Method” using a metal die, as explained below.

(Production of Sub-Mount)

A die (a master substrate) made of Ni including a recess having a depthof 250 μm for mounting the light emitting element and the light detecingelement, and a recess having a depth of 50 μm for mounting the polymerwaveguide film is molded. Using the die as the stamper (mold), lowmelting glass (made from Sumita Optical Glass Inc., “K-PG375” (Vidron),Tg: 343 deg. C., Yielding point: 363 deg. C.) is adhered to the stamper,heated for five minutes under a pressure of 10 Pa and at a temperatureof 375 deg. C., and thereafter stood to cool to cure the low meltingglass. The cured glass layer is then stripped from the stamper, therebyproducing the cured glass layer (thickness of mold: 5 mm), which surfaceincludes projections and recesses corresponding to the projections andrecesses of the stamper.

After vapor-depositing Au in a thickness of 200 nm on the cured glasslayer, the Au electrodes are patterned by photolithography, wherebyelectrode pads for lower electrodes extending from a bottom surface to aside surface of each recess up to a top surface of the sub-mount,electrode pads for upper electrodes insulated from the electrode padsfor lower electrodes are formed. By cutting the cured glass layer havingelectrode pads by using a dicer, a plurality of sub-mounts E made ofglass are formed.

Dimensional difference of projections and recesses as seen from thestamper (the master substrate) is within 100 nm, and sub-mounts E madeof glass can be produced at high precision.

(Mounting of Module) A two-way light transmission and reception modulehaving a pair of optical transmission and reception sections and apolymer waveguide film is obtained by mounting in a manner similar toExample 1 with the sub-mount E.

(Evaluation of Communication Performance)

Light transmission and reception performance of a two-way lighttransmission and reception module which is obtained according to Example3 was evaluated by using a sampling oscilloscope (product name: Agilent86100C, manufactured by Agilent Technologies) and a pulse patterngenerator. As a result, satisfactory eye pattern could be measured at upto 3.125 Gbps.

The above embodiment of the present invention provides examples of asub-mount and a light transmission and reception module having thesub-mount; however, the present invention is not limited to theembodiments, but various modifications can be made. It is obvious forthe skilled person in the art that such modifications are also includedin the scope of the invention.

A sub-mount according to the present invention has an adhesive fillinggroove formed adjacent to a recess for embedding and mounting opticalcomponents. A light transmission and reception module according to thepresent invention includes the sub-mount having the adhesive fillinggroove.

According to the above aspects, the adhesive is poured in from theadhesive filling groove arranged adjacent to the recess for mountingthereby allowing the adhesive to be evenly applied to a bottom surface(component mounting surface) of the recess for mounting when mountingthe optical component to the recess for mounting. Further, the adhesivefilling groove functions as a reservoir for liquid to prevent theadhesive from flowing out.

The light transmission and reception module uses the sub-mount includingthe adhesive filling groove adjacent to the recess for mounting to allowthe optical components such as the light detecting element or the lightemitting element to be easily and reliably mounted to the sub-mount. Thelight transmission and reception module of the present invention is thusprecise, excels in mass production, and is of low cost.

The sub-mount of the invention may be manufactured by producing a moldfor duplication formed with projections and recesses in order toreplicate a surface configuration of the sub-mount, filling a curablematerial into the produced mold for duplication, curing the curablematerial and separating the duplicated sub-mount from the mold forduplication.

According to the above, the sub-mount can be produced precisely andinexpensively.

The mold for duplication may be manufactured by applying or pouringliquid silicone rubber into the master plate of the sub-mount to becured. The mold for duplication may be manufactured by performingetching or ion reactive etching on a silicon substrate, or casting ametal.

A heat resistant resin, a light curable heat resistant resin, athermoplastic heat resistant resin and the like may be applied as thecurable material. Epoxy resin, polyimide resin and the like may beapplied as the heat resistant resin. A low-melting glass which is moltenby heating can be used. As the low-melting glass, a hard glass mainlycontaining SiO₂ and B₂O₃ can be properly applied.

According to the above, the sub-mount can be produced precisely andinexpensively.

An electrode pattern for electric wiring may be formed at the sub-mountof the invention.

An inner space of the recess for mounting is communicated with an innerspace of the adhesive filling grove in the sub-mount of the invention.

As explained above, since the adhesive filling groove is providedadjacent to the recess for mounting in the sub-mount, the adhesive canbe applied to the predetermined location precisely and prevented fromflowing out. Accordingly, the sub-mount of the invention allows easy andreliable mounting of optical components at satisfactory precision.Further, the sub-mount of the invention is precise and excels in massproduction and is inexpensive as they are manufactured by producing themold for duplication, filling the curable material into the mold forduplication and curing the curable material. The light transmission andreception module of the invention includes the sub-mount for mountingthe optical components having the adhesive filling groove thereby, theoptical components such as light detecting element or light emittingelement are easily and reliably mounted to the sub-mount at highprecision. The light transmission and reception module of the inventionis also excel in mass production with a low cost.

1. A light transmission and reception module, comprising: an opticalwaveguide film formed with an optical waveguide; a light transmittingsection having a light emitting element and a sub-mount for holding thelight emitting element, that holds one end of the optical waveguide filmon the sub-mount so that light emitted from the light emitting elemententers into an incident end surface of the optical waveguide; and alight detecting section having a light detecting element and a sub-mountfor holding the light detecting element, that holds the other end of theoptical waveguide film on the sub-mount so that light emitted from anemission end surface of the optical waveguide is detected by the lightdetecting element; wherein, each sub-mount includes a recess formounting for embedding and mounting an optical component and an adhesivefilling groove formed adjacent to the recess for mounting.
 2. The lighttransmission and reception module according to claim 1, wherein an innerspace of the recess for mounting is communicated with an inner space ofthe adhesive filling grove.